Re: [PATCH] powerpc: mark local variables around longjmp as volatile
From: Christophe Leroy
Date: Fri Jun 25 2021 - 06:35:40 EST
Le 29/04/2021 à 10:06, Arnd Bergmann a écrit :
From: Arnd Bergmann <arnd@xxxxxxxx>
gcc-11 points out that modifying local variables next to a
longjmp/setjmp may cause undefined behavior:
arch/powerpc/kexec/crash.c: In function 'crash_kexec_prepare_cpus.constprop':
arch/powerpc/kexec/crash.c:108:22: error: variable 'ncpus' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbere
d]
arch/powerpc/kexec/crash.c:109:13: error: variable 'tries' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbere
d]
arch/powerpc/xmon/xmon.c: In function 'xmon_print_symbol':
arch/powerpc/xmon/xmon.c:3625:21: error: variable 'name' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered]
arch/powerpc/xmon/xmon.c: In function 'stop_spus':
arch/powerpc/xmon/xmon.c:4057:13: error: variable 'i' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered]
arch/powerpc/xmon/xmon.c: In function 'restart_spus':
arch/powerpc/xmon/xmon.c:4098:13: error: variable 'i' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered]
arch/powerpc/xmon/xmon.c: In function 'dump_opal_msglog':
arch/powerpc/xmon/xmon.c:3008:16: error: variable 'pos' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered]
arch/powerpc/xmon/xmon.c: In function 'show_pte':
arch/powerpc/xmon/xmon.c:3207:29: error: variable 'tsk' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered]
arch/powerpc/xmon/xmon.c: In function 'show_tasks':
arch/powerpc/xmon/xmon.c:3302:29: error: variable 'tsk' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered]
arch/powerpc/xmon/xmon.c: In function 'xmon_core':
arch/powerpc/xmon/xmon.c:494:13: error: variable 'cmd' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered]
arch/powerpc/xmon/xmon.c:860:21: error: variable 'bp' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered]
arch/powerpc/xmon/xmon.c:860:21: error: variable 'bp' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered]
arch/powerpc/xmon/xmon.c:492:48: error: argument 'fromipi' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered]
According to the documentation, marking these as 'volatile' is
sufficient to avoid the problem, and it shuts up the warning.
I think this change deserves some comment in the code, and maybe also an update of
https://www.kernel.org/doc/html/latest/process/volatile-considered-harmful.html
Otherwise, there's a risk that one day or another, someone removes those 'volatile' markings.
Christophe
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
---
arch/powerpc/kexec/crash.c | 4 ++--
arch/powerpc/xmon/xmon.c | 22 +++++++++++-----------
2 files changed, 13 insertions(+), 13 deletions(-)
diff --git a/arch/powerpc/kexec/crash.c b/arch/powerpc/kexec/crash.c
index 0196d0c211ac..10f997e6bb95 100644
--- a/arch/powerpc/kexec/crash.c
+++ b/arch/powerpc/kexec/crash.c
@@ -105,8 +105,8 @@ void crash_ipi_callback(struct pt_regs *regs)
static void crash_kexec_prepare_cpus(int cpu)
{
unsigned int msecs;
- unsigned int ncpus = num_online_cpus() - 1;/* Excluding the panic cpu */
- int tries = 0;
+ volatile unsigned int ncpus = num_online_cpus() - 1;/* Excluding the panic cpu */
+ volatile int tries = 0;
int (*old_handler)(struct pt_regs *regs);
printk(KERN_EMERG "Sending IPI to other CPUs\n");
diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index c8173e92f19d..ce0eacf77645 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -489,10 +489,10 @@ static void xmon_touch_watchdogs(void)
touch_nmi_watchdog();
}
-static int xmon_core(struct pt_regs *regs, int fromipi)
+static int xmon_core(struct pt_regs *regs, volatile int fromipi)
{
- int cmd = 0;
- struct bpt *bp;
+ volatile int cmd = 0;
+ struct bpt *volatile bp;
long recurse_jmp[JMP_BUF_LEN];
bool locked_down;
unsigned long offset;
@@ -857,7 +857,7 @@ static inline void force_enable_xmon(void)
static struct bpt *at_breakpoint(unsigned long pc)
{
int i;
- struct bpt *bp;
+ struct bpt *volatile bp;
bp = bpts;
for (i = 0; i < NBPTS; ++i, ++bp)
@@ -3005,7 +3005,7 @@ static void dump_opal_msglog(void)
{
unsigned char buf[128];
ssize_t res;
- loff_t pos = 0;
+ volatile loff_t pos = 0;
if (!firmware_has_feature(FW_FEATURE_OPAL)) {
printf("Machine is not running OPAL firmware.\n");
@@ -3160,7 +3160,7 @@ memzcan(void)
printf("%.8lx\n", a - mskip);
}
-static void show_task(struct task_struct *tsk)
+static void show_task(struct task_struct *volatile tsk)
{
char state;
@@ -3204,7 +3204,7 @@ static void format_pte(void *ptep, unsigned long pte)
static void show_pte(unsigned long addr)
{
unsigned long tskv = 0;
- struct task_struct *tsk = NULL;
+ struct task_struct *volatile tsk = NULL;
struct mm_struct *mm;
pgd_t *pgdp;
p4d_t *p4dp;
@@ -3299,7 +3299,7 @@ static void show_pte(unsigned long addr)
static void show_tasks(void)
{
unsigned long tskv;
- struct task_struct *tsk = NULL;
+ struct task_struct *volatile tsk = NULL;
printf(" task_struct ->thread.ksp ->thread.regs PID PPID S P CMD\n");
@@ -3622,7 +3622,7 @@ static void xmon_print_symbol(unsigned long address, const char *mid,
const char *after)
{
char *modname;
- const char *name = NULL;
+ const char *volatile name = NULL;
unsigned long offset, size;
printf(REG, address);
@@ -4054,7 +4054,7 @@ void xmon_register_spus(struct list_head *list)
static void stop_spus(void)
{
struct spu *spu;
- int i;
+ volatile int i;
u64 tmp;
for (i = 0; i < XMON_NUM_SPUS; i++) {
@@ -4095,7 +4095,7 @@ static void stop_spus(void)
static void restart_spus(void)
{
struct spu *spu;
- int i;
+ volatile int i;
for (i = 0; i < XMON_NUM_SPUS; i++) {
if (!spu_info[i].spu)